This application bases priority on Japanese applications 2000-095806 filed Mar. 30, 2000 and 2000-286218 filed Sep. 20, 2000. The contents of both of these applications are incorporated herein by reference.
1. Field of Invention
The present invention relates to a halogen incandescent lamp using a triple-coiled filament, and a lighting apparatus using the lamp.
2. Description of Related Art
In general, a halogen incandescent lamp utilizes a coiled-coil filament, which is formed into a shorter length than that of a coiled filament. Such a filament, however, is required to be even shorter when it is used in a compact halogen incandescent lamp, for example. In order to shorten the length of a coiled-coil filament, it is known to make a coiled-coiled-coil or a triple-coil filament by winding a coiled-coil filament around a mandrel.
Such a triple-coiled filament can generate radiation close to a point source of visible light. When a lighting apparatus including a reflector is provided with such a halogen incandescent lamp having the triple-coiled filament, it is easy to position the triple-coiled filament around a focus of the reflector. Therefore, visible light generated by the triple-coiled filament is accurately reflected by the reflector. Furthermore, the visible light can accurately irradiate a predetermined area, so that the lighting apparatus has an improved light output ratio. In contrast, the lamp life of such a triple-coiled filament is occasionally short because of sagging and therefore, shorting, during lamp operation.
Japanese Laid Open Utility model Application SHO 58-6369, U.S. Pat. No. 4,499,401 (the ""401 patent), and U.S. Pat. No. 4,316,116 (the ""116 patent) disclose such a triple-coiled filament for an incandescent lamp. In particular, a triple-coiled filament, described in the ""401 patent, has dimensions selected so that it does not require re-crystallization prior to the triple-coiled filament being arranged within the incandescent lamp, simplifying manufacturing. That is, an outer diameter of the triple-coiled filament is in a range of 20d to 26d, wherein d is a diameter of the tungsten wire. As a result, the triple-coiled filament does not sag during lamp operation, because of its small outer diameter. Therefore, separated windings of the triple-coiled filament do not easily come into contact with each other, avoiding a short circuit. However, when the outer diameter of the triple-coiled filament is in the range of 20d to 26d, the length of the filament tends to become long because the outer diameter of the filament is shortened. Therefore, it is not easy to apply this filament to a compact halogen incandescent lamp or to position the triple-coiled filament around the focus of the reflector.
Furthermore, the ""401 patent explains that the triple-coiled filament of the ""116 patent having an outer diameter 27d, wherein d is a diameter of a tungsten wire, necessitates a re-crystallization process to eliminate sagging during lamp operation. That is, the grain size of the crystals in the filament grows, so that the re-crystallized triple-coiled filament becomes stronger. However, the elasticity of such a re-crystallized triple-coiled filament decreases excessively, so that it more likely to be damaged by impact. Therefore, when the re-crystallized triple-coiled filament receives an impact from the outside, for example, the re-crystallized triple-coiled filament may vibrate and occasionally break, for example, at the interface of the grains of the crystal.
According to one aspect of the invention, a halogen incandescent lamp comprises a light-transmitting envelope filled with a gas including a halogen gas and an inert gas. A pair of inner conductive wires are arranged in the envelope. A triple-coiled filament, which has a first coiling, a second coiling, and a third coiling having about 1.5 to about 4 turns, is re-crystallized, arranged in the envelope, and connected between ends of the inner conductive wires. The triple-coiled filament is held by a support member.
According to another aspect of the invention, a lighting apparatus comprises the halogen incandescent lamp described above having a reflector, and a housing accommodating the lamp.